How to Optimize Your Performance: Sweat Rate and Optimizing Hydration

There are several components that make a race day plan when preparing for your triathlon: a good race strategy/pacing plan, fueling (pre-race and then carbs per hour during), and hydration (amount of fluid and electrolytes per hour).  The two key components of a good hydration plan are knowing your sweat rate and the sweat sodium content of your sweat.  These two get confused often, but they are not the same thing.   Just because you sweat a lot, it does not mean that you are a necessarily a “salty sweater”.   Or, you could have a high sweat rate and still be a very salty sweater.  As a coach, I’ve work with athletes to fix their nutrition plan and have seen as much as 1:30-2 hours come off of their Ironman time based off of better hydration and electrolyte usage!  Athletes must navigate varying environmental conditions and exertion levels on race day, which significantly affect their sweat rate and sodium loss. Understanding these factors is key to optimizing performance and avoiding dehydration-related issues.

Sweat rate refers to the volume of sweat an athlete loses per unit of time, typically measured in liters per hour. This rate can vary widely depending on factors such as environmental temperature, humidity, exercise intensity, and individual physiology.  In hot and humid conditions, triathletes can sweat profusely to dissipate heat and maintain a stable core temperature.  In colder temperatures, the same athlete would typically lose much less.  For example, an athlete may lose 1.5-2 L per hour on the run in hot conditions, and only .5 L per hour at the same intensity in cooler temperatures.

The good news is: figuring out your sweat rate is actually very easy!  To figure out your sweat rate:  weigh yourself pre-workout and then again post-workout with as little clothing on as possible and record the numbers.  Multiply the pounds lost by 16 to figure out how many ounces of sweat you lost.  Also record the amount of fluid consumed during the workout.  Then, use this equation:

(_______ fluid ounces consumed + ________ fluid ounces lost (lbs lost)  ÷ _______  hours of workout  =________ fluid ounces needed each hour

For example:   20 oz consumed + 32 oz lost (2 lbs) ÷ 2 hour workout = 26 oz/hour needed

Pro tip:  keep a running journal/log noting the different temperatures and intensities of your workouts.  Knowing the approximate sweat rate that will be similar to race day will make it much easier to figure out a good hydration plan.

Sweat sodium content is measured in the amount of milligrams of sodium per liter of sweat lost.  This number is different for everyone and is influenced by genetics, training adaptation, and diet. Sodium is a crucial electrolyte lost through sweat, and its concentration can range from as little as 300 to 2,000+ mg per liter.  In endurance events, excessive sodium loss can lead to hyponatremia (low blood sodium levels), muscle cramps, GI problems, and it can affect your ability to digest your fuel. 

The only way to know your sweat sodium number is to take a test.  There are two companies offering this test:  Levelen (via mail) and Precision Hydration (in person). 

1. Pre-Hydration: Begin races well-hydrated by consuming fluids containing electrolytes in the hours leading up to the event.
2. During: Regularly assess fluid intake based on your sweat rate, demands, and environmental conditions. Aim to replace fluids lost while balancing electrolyte needs via sport drinks and salt tabs or capsules
3. Rehydration: Replenish fluids and electrolytes promptly after racing or workouts to support recovery and maintain hydration status for subsequent training or races.
4. Individual Variation: Monitor sweat rate and sodium concentration through training sessions to tailor hydration plans to individual needs. Factors such as heat acclimatization, sweat adaptation, and dietary sodium intake influence these requirements.

Once you know these two numbers, then you will be able to adapt your strategy based on environmental conditions, race intensity, and your individual physiology to maintain peak performance and avoid dehydration-related complications for race day success!